Vehicles may operate on a wide variety of road surfaces to take passengers to their desired destinations. The vehicles may also be stopped and restarted at a later time on these road surfaces. For example, a vehicle may be stopped and parked on a hill so that the vehicle is directed uphill or downhill. If the hill has a high grade, the vehicle may roll uphill or downhill assisted by the grade after the engine is started when the vehicle's transmission is disengaged from park. The vehicle's driver may prevent or reduce vehicle acceleration after the transmission is disengaged from park by applying vehicle brakes. However, if the vehicle is an automatically stopped and started vehicle, applying the vehicle brakes may cause the vehicle's engine to stop when the driver is preparing to drive away since engine starting may be dependent on vehicle brake application. On the other hand, if the driver releases the brake to restart the engine, the vehicle may accelerate in a downhill direction. In this way, stopping an automatic start/stop vehicle on a hill may allow a vehicle to move when the driver simply intends for the engine to start. Therefore, it may be desirable to determine whether or not a vehicle is stopped on a hill so that mitigating actions to limit vehicle movement may be taken.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for operating a vehicle, comprising: applying or adjusting an actuator in response to a rolling direction estimated from a correlation coefficient based on an unsigned wheel speed and a sign specific vehicle longitudinal acceleration.
By adjusting an actuator in response to a vehicle rolling direction and/or road grade, it may be possible to mitigate the possibility of vehicle motion during automatic engine starting. Further, system cost may be reduced when unsigned wheel speed sensors are a basis for determining vehicle rolling direction and road grade. For example, if there is observed a positive correlation between not sign specific wheel speed based vehicle acceleration and sign specific accelerometer (e.g., an accelerometer output that includes a sign) based vehicle acceleration, it may be determined that the vehicle is rolling in a forward direction. If a negative correlation between not sign specific wheel speed based vehicle acceleration and sign specific accelerometer based vehicle acceleration is established, it may be determined that the vehicle is rolling in a reverse or backward direction. The rolling direction may be input into a kinematic equation to establish road grade, and the road grade may allow actuators to adjust engine torque and vehicle brakes to compensate for gravitational forces.
The present description may provide several advantages. Specifically, the approach may allow an engine to be automatically started without causing the vehicle to move when the vehicle is stopped on a hill. Further, the approach may provide rolling direction and road grade without having to use signed wheel speed sensors, thereby reducing system cost. Further still, the approach may allow engine torque actuators to be adjusted to a level to oppose gravitational forces without producing unnecessary engine torque.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.